package demo1;

import java.util.List;

public class MyLinkedList {
    //LinkedList的底层其实就是双向链表结构
    static class ListNode{
        private int val;
        private ListNode prev;
        private ListNode next;

        public ListNode(int val) {
            this.val = val;
        }
    }

    public ListNode head;
    public ListNode last;

    //底层的方法实现
    //得到双向链表的长度
    public int size(){
        ListNode cur = head;
        int count = 0;
        while (cur!=null){
            count++;
            cur = cur.next;
        }
        return count;
    }
    //遍历双链表
    public void display(){
        ListNode cur = head;
        while(cur!=null){
            System.out.print(cur.val+" ");
            cur = cur.next;
        }
        System.out.println();
    }

    //查找是否包含关键字key是否在单链表当中
    public boolean contains(int key){
        ListNode cur = head;
        while(cur!=null){
            if (cur.val == key){
                return true;
            }
            cur = cur.next;
        }
        return false;
    }
    //头插法
    public void addFirst(int data){
        ListNode node = new ListNode(data);
        if (head == null){
            head = node;
            last = node;
            return;//不要忘记
        }
        node.next = head;
        head.prev = node;//当链表当中一个节点都没有的时候就会出现空指针异常
        head = node;
    }
    //尾插法
    public void addLast(int data){
        ListNode node = new ListNode(data);
        if (head == null){
            head = node;
            last = node;
            return;
        }
        last.next = node;
        node.prev = last;
        last = node;
    }
    //任意位置插入,第一个数据节点为0号下标
    public void addIndex(int index,int data){
        if (index<0||index>size()){
            throw new IndexOutOfBoundsException("双向链表index不合法！");
        }
        ListNode node = new ListNode(data);
        if (index == 0){
            addFirst(data);
            return;
        }
        if (index == size()){
            addLast(data);
            return;
        }
        ListNode cur = head;
        while (index != 0) {
            cur = cur.next;;
            index--;
        }
        node.next = cur;
        cur.prev.next = node;
        node.prev = cur.prev;
        cur.prev = node;
    }

    //删除第一次出现关键字为key的节点
    public void remove(int key){
        ListNode cur = head;
        while (cur!=null){
            if (cur.val == key){
                if (cur == head){
                    head = head.next;
                    //如果链表里面不只有一个节点
                    if (head!=null){
                        head.prev = null;
                    }else {
                        last = null;
                    }
                }else{
                    cur.prev.next = cur.next;
                    if (cur.next != null){
//                        cur.prev.next = cur.next;
                        cur.next.prev = cur.prev;
                    }else {
//                        cur.prev.next = cur.next;
                        last = last.prev;
                    }

                }
                return;
            }else{
                cur = cur.next;
            }
        }
    }
    //删除所有值为key的节点
    public void removeAllKey(int key){
        ListNode cur = head;
        while (cur!=null){
            if (cur.val == key){
                if (cur == head){
                    head = head.next;
                    //如果链表里面不只有一个节点
                    if (head!=null){
                        head.prev = null;
                    }else {
                        last = null;
                    }
                }else{
                    cur.prev.next = cur.next;
                    if (cur.next != null){
//                        cur.prev.next = cur.next;
                        cur.next.prev = cur.prev;
                    }else {
//                        cur.prev.next = cur.next;
                        last = last.prev;
                    }
                }
            }
            cur = cur.next;//困惑的地方:如果当前cur所在节点满足val为key，那么删掉了之后还怎么找next????
        }
    }

    public void clear(){
        public void clear(){
        //head = null;
        //last = null;
        ListNode cur = head;
        while(cur!=null){
            ListNode curNext = cur.next;
            cur.prev = null;
            cur.next = null;
            cur = curNext;
        }
        head = null;
        last = null;
    }
    }
}
